1. Technical field
The embodiments herein generally relate to the field of wireless communication and particularly relate to techniques of sending system information messages in wireless communication systems. The embodiments herein more particularly relates to a method of acquiring multiple system information messages in a single system information window without any ambiguity or loss of system information.
2. Description of the Related Art
The Long Term Evolution (LTE) is a new terrestrial mobile communication standard currently being standardized by the 3GPP. The Radio Access Network. (RAN) of LTE is named as the Evolved-Universal Mobile Telecommunication Systems Radio Access Network. (E-UTRAN). The E-UTRAN physical layer is based on Orthogonal Frequency Division Multiplexing (OFDM). More precisely; the downlink
transmission scheme is based on conventional. OFDM using a cyclic prefix while the uplink transmission is based on single carrier frequency division multiple access (SC-FDMA) techniques. The OFDM subcarrier spacing is 15 kHz in both uplink and downlink transmission. LTE supports both frequency division duplex (FDD) and time division duplex (TDD).
System Information (SI) in an LTE system is divided into a number of System Information Blocks (SIBs) and Master Information Block (MIB). The MIB includes limited number of most essential and frequently transmitted parameters to acquire other information from the cell. The SI is defined in TS 36.300 as a RRC message carrying a number of System Information Blocks (SIBs) that have the same periodicity. Each System Information Block (SIB) contains a set of related system information parameters. SystemInformationBlockType1 (SIB1) is transmitted alone, separately from other SI-messages. The MIB message is mapped on a Broadcast Control Channel (BCCH) and carried on Physical Broadcast Channel (PBCH). All other SI messages are carried on a Downlink Shared Channel (DL-SCH) where they can be identified through the SI-RNTI (System Information Radio Network; Temporary Identifier).
SIBs other than SIB1 are carried in SI messages and mapping of System Information Blocks to SI messages is flexibly configurable by using a scheduling Information parameter included in SIB1, with restrictions that each SIB is contained only in a single SI message. Only SIBs having the same scheduling (periodicity) requirement can be mapped to the same SI message. SystemInformationBlockType2 (SIB2) is always mapped to the SI message that corresponds to the first entry in the list of SI messages in the scheduling information parameter.
Multiple SI messages may be transmitted with the same periodicity. The MIB uses a fixed schedule with a periodicity of 40 ms and repetitions made within 40 ms. The first transmission of the MIB is scheduled in subframe #0 of radio frames for which the System Frame Number (SFN) mod 4=0 arid repetitions are scheduled in subframe #0 of all other radio frames. The SIB1 uses a fixed schedule with a periodicity of 80 ms and repetitions made within 80 ms. SIB1 is scheduled in subframe #5 of radio frames for which SFN mod 8=0 and repetitions are scheduled in subframe #5 of all other radio frames for which SFN mod 2=0.
The SI messages are transmitted with periodically occurring time domain windows (referred to as SI-windows) using a dynamic scheduling mechanism. Each. SI message is associated with a SI-window and the SI-windows of different SI messages do not overlap. That is, within one SI-window only the corresponding SI is transmitted. The length of the SI-window is common for all SI messages and is configurable. Within the SI-window, the corresponding SI message can be transmitted a number of times in any subframe other than sub-frames where SIB1 is present (i.e. subframe #5 of radio frames for which SFN mod 2=0), any uplink subframes in TDD and any MBSFN subframes, SIB1 configures the SI window length and the transmission periodicity for the SI messages. For TDD networks, SIB1 configures TDD configuration which includes subframe Assignment and special Subframe Configuration. SIB2 configures the MBSFN-Subframe Config which defines subframes that are reserved for MBSFN in downlink.
A user equipment (UE) acquires the detailed time-domain scheduling (and other information e.g. frequency-domain scheduling, information on the used transport format etc.) from decoding the SI-RNTI on Physical Downlink Control Channel (PDCCH). A single SI-RNTI is used to address SIB1 as well as other SI messages. The UE acquires SIB1 and other SI messages on the Physical Downlink Shared Channel (PDSCH) resource indicated by decoding PDCCH.
Normally, in System Information (SI) message acquisition procedure, the UE acquires only one SI message in a SI window resulting in ambiguity and loss of System Information when SI windows of multiple SI messages overlap.
In view of the foregoing, there exists a need for an efficient method and system for acquiring multiple system information messages in a single system information window. There also exists a need for a method and system for providing flexibility in the scheduling of System Information messages. Further, there exists a need to provide a method and system for acquiring multiple system information messages in a single system information window without any ambiguity or loss of system information.
The above mentioned shortcomings, disadvantages and problems are addressed herein and which will be understood by reading and studying the following specification.